The present invention relates to a method and apparatus for cleaning various machinery and devices used in nuclear plants and more particularly relates to a method and apparatus for cleaning such machinery and devices by blasting dry-ice particles under the presence of ice particles or a surface-active agent.
The conventional cleaning methods of that kind may be roughly divided as follows:
(1) Sand blasting method in which sand particles are blown under high pressure against machinery or devices to be cleaned;
(2) Dry-ice blasting method in which dry-ice particles are blown against machinery or devices to be cleaned;
(3) Ice blasting method in which ice particles are blown against machinery or devices to be cleaned;
(4) Water blasting method; and
(5) Liquefied-freon blasting method.
When the sand blasting method is used to clean the machinery and devices of nuclear plants, sand particles blown against the surfaces of these machinery and devices become radioactive waste contaminants so that there arises a problem how to dispose such radioactive waste contaminants. Furthermore, radioactive contaminants are caused to be scattered by dust particles so that there must be provided a method for preventing dust particles from scattering.
In the case of the dry-ice blasting method, the dry-ice particles are vaporized so that the object to be cleaned cannot be seen and consequently the cleaning procedure is adversely affected.
In the case of the ice blasting method, the ice particles are blown against the object to be cleaned. The density of ice is lower than that of dry ice so that the ice blasting method is not so efficient in cleaning efficiency as the dry-ice blasting method.
In the case of the water blasting method, the cleaning efficiency is very low. Moreover, because of a vast amount of water being used, it is very difficult to effect disposal of radioactive waste water.
In the case of the liquefied-freon blasting method in which the liquefied-freon is blasted and the waste freon is vaporised and is withdrawn, the cleaning efficiency is low.
The present invention therefore provides a cleaning method and apparatus in which scattering of dust particles can be prevented and screening by sublimation of dry ice can be prevented so that efficient cleaning of various machinery and devices can be carried out. According to the present invention, dry-ice particles are blasted under high pressure and in the presence of ice particles or a surface-active agent against the surfaces of an object to be cleaned, so that the scattering of radioactive contaminants into the atmosphere can be prevented.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.